AMPLITUDE-PHASE-KEYING WITH M-ARY ALPHABETS: A TECHNIQUE FOR BANDWIDTH REDUCTION

Abstract

The spectral occupancy of transmitted digital data can be reduced by employing symbols from an M-ary alphabet. A modulation technique combining both amplitude and phase keying (APK) requires less peak and average power than M-ary PSK to achieve the same symbol error probability. Efficient signal set designs have been found by an empirical search of a large number of candidate sets with a comparison based on symbol error probability. New 8-ary and 16-ary designs are presented which outperform previously suggested designs on both a peak and average SNR basis. The bandwidth efficiency of the principal APK sets and PSK is presented as a function of alphabet size (4-ary to 128-ary) to illustrate the bandwidth-power tradeoff.